1. Technical Field
The present invention relates to a fiber manufacturing apparatus that manufactures fibers by using an electrospinning method (an electrostatic stretching phenomenon), and especially relates to a fiber manufacturing method and a fiber manufacturing apparatus that can add various types of functions to fine fibers of which diameter is in a nano order (nano-fibers).
Moreover, the present invention relates to a fiber manufacturing method for manufacturing fibers that make up a catalyst substance layer used as a fuel electrode or an oxygen electrode for a proton-exchange membrane fuel cell.
2. Background Art
Conventionally, an electrospinning (an electrostatic stretching phenomenon) method is known as a method for manufacturing filamentous (fibrous form) substances (nano-fibers) made of polymeric substances and having a diameter in a submicron scale.
In the electrospinning method, raw material liquid in which polymeric substances and such are dispersed or dissolved in a solvent medium is injected (outpoured) to a space, through a nozzle or such, while the raw material liquid is charged by applying an electric charge and the raw material liquid that flies in the space is electrostatistically exploded, so that nano-fibers can be obtained.
More specifically, regarding the raw material liquid that is electrically charged and outpoured, as the solvent medium is evaporated from the raw material liquid flying in the space, volume of the raw material liquid decreases. On the other hand, the electric charge applied to the raw material liquid remains in the raw material liquid. As a result, a particle of the raw material liquid flying in the space is made to a higher electric charge density. Moreover, because the solvent medium in the raw material liquid keeps evaporating on an ongoing basis, the electric charge density of the raw material liquid is further increased, and the polymer solution undergoes a phenomenon (an electrostatic stretching phenomenon) in which the polymer solution is explosively stretched into filament at a point when coulomb force acting oppositely generated in the raw material liquid exceeds the surface tension power of the raw material liquid. Because this electrostatic stretching phenomenon occurs one after another at an exponential rate in the space, fibers (nano-fibers) made of polymeric substances of which diameter is in a submicron scale (for example, see Japanese Unexamined Patent Application Publication No. 2005-330624) is manufactured.
The fibers manufactured by the above electrospinning method are used as a raw material for a string or a nonwoven fabric cloth. Additionally, there has been an attempt to improve functionality of the string or the nonwoven fabric cloth by having the nano-fibers carry functional substances such as a catalyst or an absorbent substance.
For example, an applicant of the present invention has filed a manufacturing method of nano-fibers carrying a carried material through manufacturing such nano-fibers by pre-mixing a functional carried material into raw material liquid and manufacturing nano-fibers from the concerned raw material liquid through the electrospinning method.
In addition, a power fuel cell has been drawing attention in recent years. The reason for that is as follows. Namely, the fuel cell, contrary to its name, is not like a battery that electrically discharges pre-charged power such as a primary cell like a dry-cell battery or a secondary cell like a lead acid battery. It is something closer to a power generation apparatus that allows us to take out the power on an on-going basis if a fuel such as hydrogen and an oxidizing agent such as oxygen are supplied continuously. The fuel cell is not like a conventional power generation apparatus that uses a thermal engine and it allows for obtaining of electric energy directly from chemical energy without going through motion energy, so that it has a high power generation efficiency with less noise and less vibration. Therefore, it is expected to be used as a power source of a portable apparatus, a power source for domestic use or a power source of automobiles, trains and so on.
The following actions are taken as a method to generate power by the fuel cell. In short, in a catalyst substance layer of a fuel electrode, hydrogen is divided into an electron and a proton (a hydrogen ion) by using a catalyst substance. The divided electron is supplied to the outside of the fuel cell via an electric conductor. The proton is moved to an oxygen electrode via a proton conductive polymer within the fuel cell. The proton going through the proton conductive polymer reacts with oxygen in the solvent layer of the oxygen electrode and turns into water, but because it requires an electron at this point, the electron conveyed to the outside of the fuel cell is collected and provided for the aforementioned reaction.
Consequently, a difference in an electric potential is created between the fuel electrode, which has an excessive amount of electrons, and the oxygen electrode, which requires more electrons, and the power can be generated.
As described above, in order for hydrogen to be divided into an electron and a proton in the catalyst substance layer of the fuel electrode, and for the proton, oxygen and the electron to react and turn into water in the catalyst substance layer of the oxygen electrode, it is necessary that the oxygen makes contacts with the catalyst substance, and that the proton, the oxygen and the electron make contacts among themselves. Moreover, in order to move the electron, it is necessary to have an electric conductor close to the aforementioned catalyst substance. In order to move the proton, it is necessary to have a proton conductive polymer close to the catalyst substance.
Furthermore, for improving a power generation efficiency of the fuel cell, it is necessary to be the location where the catalyst substance, the electric conductor and the proton conductive polymer all coexist. In the catalyst substance layer of the fuel electrode, it is necessary to have many locations with a high probability for making contacts with hydrogen, and in the catalyst substance layer of the oxygen electrode, it is necessary to have many locations with a high probability for making contacts with oxygen.
Conventionally, the following method has been proposed to form the catalyst substance layer as described above (see Japanese Unexamined Patent Application Publication No. 2007-214008). In short, a carbon carrying a catalyst substance and a proton conductive polymer are put in the solvent medium and made into a liquid form. The concerned liquid is injected from one electrode to another electrode to which high voltage is applied. As described above, an electrostatic stretching phenomenon is created, and fibers made of the proton conductive polymer that carries the catalyst substance and the carbon are manufactured. A porous catalyst substance layer is formed by depositing the concerned fibers.
However, as an inventor of the present invention further researched the aforementioned fiber manufacturing method, the inventor discovered there is a case that fibers having a desired function are difficult to manufacture depending on a type of a resin consisting of fibers or a type of a carried material to be carried. As the inventor was dedicated to doing further research, the inventor discovered there is a case that the carried material cannot perform its function because the carried material is contained within the fibers, and there is a case that a mechanical strength of the fibers is weakened because the carried material is intruded into the fibers too much.
Also, for the fuel cell, in the aforementioned method, the catalyst substance is built in the proton conductive polymer in a process the proton conductive polymer is turned into fibers so that there are so many catalyst substances that do not make contacts with hydrogen or oxygen and are not provided for reaction necessary for power generation. The fuel cell containing such a catalyst substance layer does not have a good power generation efficiency as it is compared to an amount of the catalyst substance used.